1. Technical Field
This invention relates generally to programmable amplifiers and, more particularly, to an integrated transducer amplifier circuit having amplifier characteristics such as gain and offset which may be programmed following final assembly of a packaged sensor.
2. Discussion
Transducers are commonly used to produce an electrical signal in response to a force and may be configured to sense pressure or motion/acceleration, for example. Piezoresistive transducers are conventionally configured with strain sensing circuit elements fabricated on a semi-conductor chip. Since piezoresistive transducers are generally known to produce very small outputs, the transducer outputs typically must therefore be sufficiently amplified. The necessary amplification is usually accomplished with a specialized transducer amplifier.
When amplifying a transducer output, the specialized transducer amplifier realizes certain gain and offset characteristics of the amplifier. It is generally preferred that these amplifier characteristics match those of the transducer element being amplified so as to realize the desired response. In high volume manufacturing applications, it is desired to configure the amplifier so that the amplifier characteristics can be individually adjusted to match the variations present in the transducer element. This is often necessary since variations often do occur over normal manufacturing production runs.
In the past, amplifier characteristics such as gain and offset have been individually calibrated by employing a laser trimming approach. According to this approach, laser trimming resistor elements are carefully trimmed with a laser so as to adjust the resistance value of resistor networks. Alternately, fusible links have also been used to adjust the value of the resistor networks. For motion or pressure sensing transducers, it is sometimes a requirement that the calibration process be performed during the application of the appropriate physical stimulus of motion or pressure. Furthermore, the conventional resistor trimming operation generally requires physical access to the resistors which are otherwise normally enclosed or encapsulated by the final packaged sensor housing. It is therefore required that the laser trimming calibration process be performed prior to the final assembly operations of the sensor and amplifier circuit. The transducer is thereafter fully assembled and then tested. Calibration of an amplifier prior to final assembly usually requires an additional processing step which adds to the overall manufacturing time and cost.
It is therefore desirable to provide a programmable transducer amplifier circuit which may be easily programmed so as to calibrate amplifier characteristics such as gain and offset.
More particularly, it is desirable to provide a programmable transducer amplifier circuit which may be electrically programmable to adjust amplifier characteristics after final assembly of the transducer package and without requiring physical access to assembled components.
It is further desirable to provide for such a programmable transducer amplifier circuit which may be easily programmable via application of electronic signals so as to match gain and offset characteristics to those of the transducer element.
Yet, it is also desirable to provide for such a programmable transducer amplifier circuit and method for programming an amplifier so as to calibrate for characteristics thereof to compensate for changes such as temperature effects.